β‐Crystallins (β1,‐, β2‐ and β3‐crystallin) comprise nearly half the protein of the human lens. The effect of near‐UV radiation, which is one of the possible risk factors in cataract formation, on the p‐crystallins is investigated in this study. Protein intersubunit crosslinking, change in charge of the protein subunits to more acidic species and changes in protein tertiary structure (conformation) by 300 nm irradiation are reported. The fluorescence yield of protein tryptophan residues decreases by 300 nm irradiation. There is an increase in nontryptophan fluorescence (λcx 340 nm, λcm 400–600 nm), and in protein absorption at 340 nm, due to the formation of tryptophan photooxidation products. Both tryptophan and its oxidation products can be photoexcited by 300 nm irradiation and the latter are known to be good photosensitizers. The results provide evidence for the generation of H202 in the irradiated human β‐crystallin solutions by the Type I photosensitizing action of the chromophores absorbing at 300 nm. The H2O2 is generated via the intermediate production of O‐2 anion; the latter spontaneously dismutates to H202, presumably via O ‐2 ‐ protein interactions. The amount of H2O2 generated per absorbed photon is compared for various solutions of β1,‐, β2‐ and β3‐crystallins from human lenses of different age.
|Number of pages||9|
|Journal||Photochemistry and Photobiology|
|State||Published - Jul 1989|